Phase-locked electric machines, in which the rotor has the same rotational frequency as the stator rotational field, generate a torque which depends greatly on the angular offset between the rotor and the stator rotational field. Furthermore, there are numerous applications for electric machines in which the angular position of the drive shaft of the electric machine must be synchronized with the output, for example for use as a starter for internal combustion engines to whose camshaft a torque is applied, for a successful start it being necessary to precisely take the angular position of the camshaft into account.
Numerous conventional angle sensors for angle detection are manufactured separately from the electric machine and are mounted on the electric machine only after the latter is manufactured. This is the case in particular for hybrid drives, in which the angle sensor is first connected to the electric machine during assembly of the traction module (initial pairing) or during replacement of the electric machine or the angle sensor (component replacement for repairs, for example). Since the electric machine, which for hybrid drives is usually a synchronous machine, has already been provided with a stator and a housing after manufacture, only the shaft is accessible, and it is very difficult to ascertain the angular position of the rotor, in particular in relation to the starter windings. Due to the compact design of a traction module it is also complicated and difficult to mount an angle sensor on the synchronous machine at an accurate angle using markings. For initial pairing and for component replacement it is therefore difficult to accurately install the sensor on the shaft of the electric machine with high precision.
German Patent Application No. DE 10 2005 056 207 A1 describes a sensor system having multiple mutually offset sensor elements which may be adapted to various shaft diameters. However, the sensor elements allow only the relative angle to be ascertained in order to determine the angular velocity, and the determination of the absolute angle, taking an offset angle into account, is not considered.
The pairing of the angle sensor with the electric machine after these two components are manufactured thus results in an error angle, referred to as the “offset angle,” due to which the phase-accurate control of the electric machine is inexact. For phase-locked electric machines such as synchronous motors, the actual torque is not accurately controllable due to the offset angle.